A pterygium is an elevated, superficial, external ocular mass that usually forms over the cornea, and particularly in Bowman's layer. Pterygia can vary from small, atrophic quiescent lesions to large, aggressive, rapidly growing fibrovascular lesions that can distort the corneal topography, and, in advanced cases, obscure the optical center of the cornea. Growth is typically in a triangular shape.
The pathophysiology of pterygia is characterized by degeneration of collagen and fibrovascular proliferation, with an overlying covering of epithelium. It is believed that pterygium cells may produce elevated levels of matrix metallopeptidase (MMP), including specifically MMP-1, MMP-2, and MMP-9. Proteins of the MMP family are involved in the breakdown of extracellular matrix in normal physiological processes, such as embryonic development, reproduction, and tissue remodeling. It is believed that the over-expressed MMP's are responsible for the dissolution of Bowman's layer.
Occurrence of ptyerigium varies with geographical location. Within the continental United States, prevalence rates vary from less than 2% above the 40th parallel to 5-15% in latitudes between 28-36°. Outside of the U.S., a similar relationship is seen between incidence of pterygium and geographical location. There is a relatively high incidence of pterygium in the countries of the Middle East. A relationship is thought to exist between increased prevalence of pterygium and elevated levels of ultraviolet light exposure in the lower latitudes. There may also be a genetic predisposition to the formation of pterygia.
Pterygia can cause a significant alteration in visual function in advanced cases. They also can become inflamed, resulting in redness and ocular irritation. Medical therapy of inflammation-causing pterygia consists of application of over-the-counter artificial tears/topical lubricating drops (eg, Refresh Tears®, GenTeal® drops) and/or bland, non-preserved ointments (eg, Refresh P.M.®, Hypo Tears®), as well as occasional short-term use of topical corticosteroid anti-inflammatory drops (eg, Pred Forte® 1%) when symptoms are more intense. However, such treatments address the inflammation symptoms only, and do not interfere with the growth of the pterygium. A pterygium that is large enough to impair sight or is unsightly may need to be removed surgically.
Pterygium is one example of a pathology associated with increased MMP production. Other such pathologies include Kerataconus, macular degeneration, corneal melting, occlusions in the choroid, cancer and heart disease.
A need exists for a non-surgical treatment for pterygium and other MMP-implicated pathologies, as well as a less toxic adjunct for pterygium, glaucoma and vitreo-retinal membranes}